Field Crops Research 217 (2018) 167–171

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Field Crops Research

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A study on the productivity under the continuous cultivation in T Province, I. Yield trend under continuous maize cultivation

Kazuhiko Fujisaoa, Phanthasin Khanthavongb, Saythong Oudthachitb, Naruo Matsumotoc, ⁎ Koki Hommad, , Hidetoshi Asaic, Tatsuhiko Shiraiwaa a Graduate School of Agriculture, Kyoto University, Kitashirakawa-Oiwake, Sakyo, Kyoto, Kyoto 606-8502, Japan b National Agriculture and Forest Research Institute, Nongvienkham, Xaythany, Capital 811, Lao Democratic People’s Republic c Japan International Research Center for Agricultural Sciences, 1-1 Ohwashi, Tsukuba, Ibaraki 305-8686, Japan d Graduate School of Agricultural Science, Tohoku University, Aramaki Aza-Aoba, Aoba, Sendai, Miyagi 980-0845, Japan

ARTICLE INFO ABSTRACT

Keywords: Continuous maize cropping has increased in Laos. Because maize is continuously cultivated without fertilizer or Maize any soil conservation practices, there is a concern that maize yield is decreasing. In this study, we conducted a Continuous cropping field survey and interviews with farmers to quantify maize production sustainability under continuous culti- Yield vation in relation to topographical characteristics in farmers’ fields within Sainyabuli Province, Laos. Yield was Sustainability investigated over a two-year period at three sample sites in each of the 40 farmers’ fields, including sloped and Mountainous area flat fields. In addition, to analyze the difference in yield trend due to topo-sequential position, the sample sites were categorized into four topo-sequential positions per slope angle and relative elevation: “upper,”“middle,” and “lower” positions for sloped fields and “flat” for flat fields. The period of continuous maize cultivation in each field varied from 1 to 30 years. The average yield of the three sample sites in each field varied from 1.1 to − 6.0 t ha 1 and tended to be lower as the period of continuous cultivation was longer. ANCOVA and regression analysis for each topo-sequential position indicated that the decreasing yield trend in each field were mainly − derived from the upper position of sloped fields. Cost of 1.7 t ha 1, in terms of maize yield, were required for purchasing seed, herbicide, and outsourcing plowing in maize cultivation. The linear regression line of the yield based on the period of continuous cultivation suggested that maize production decreased at − − −0.06 t ha 1 year 1; but it could be economically viable for 43 years. However, yield in six of the 36 fields was evaluated as below profitable levels, indicating that urgent improvements in field and crop management are required to produce maize sustainably.

1. Introduction decomposition of soil organic matter (Raich and Schlesinger, 1992). Accordingly, rapid decreases in maize yield have been commonly an- Increasing population and the pursuit of cash incomes have in- ticipated in the tropical zone. Anthony et al. (1995) reported that yields − tensified crop cultivation in upland fields of Southeast Asia. The area of decreased by 4.5 t ha 1 over nine years from a fertilization experiment continuous crop cultivation has increased while the area of traditional in Nigeria. Sileshi and Mafongoya (2006) reported that yields decreased − shifting cultivation has decreased (Thongmanivong and Fujita, 2006; by 2.0 t ha 1 over four years from an experiment in Zambia. Moebius- Vliet et al., 2012). Notably, in Laos, the harvested area for maize in- Clune et al. (2011) assessed yield from several farmers’ fields in Kenya, − creased from 44,956 ha in 2002–214,460 ha in 2014. Maize became one and estimated that yield decreased about by 2 t ha 1 over 12 years. On of the major cash crops in Laos and is primarily produced in the the contrary, over 30 years of maize production in Laos seems not to northern mountainous areas. Kenthao District in Sainyabuli Province is follow the above examples, although maize was commonly cultivated the one of leading districts for maize production, where the continuous via continuous cropping without any external input of fertilizer or soil cultivation has been conducted for over 30 years. conservation practices. The evaluation of sustainability in maize pro- In general, soil is easily degraded in tropical zones. High rainfall duction is quite important to forecast future production in the country intensity is frequently observed during the rainy season, which in- and in places where maize production is introduced, instead of shifting creases erosion and causes rapid soil degradation (Wischmeier and cultivation. However, to our knowledge, scientific study regarding Smith, 1958). High temperature also increases the rate of maize production in farmers’ fields in Laos is quite limited.

⁎ Corresponding author. https://doi.org/10.1016/j.fcr.2017.12.016 Received 30 September 2017; Received in revised form 14 December 2017; Accepted 14 December 2017 Available online 27 December 2017 0378-4290/ © 2017 Elsevier B.V. All rights reserved. K. Fujisao et al. Field Crops Research 217 (2018) 167–171

Scientifically, long-term trends of soil condition and crop yields are September). Because the precipitation in the dry season is inadequate, often analyzed by chronosequence methods, which compare target most farmers plant one crop per one year only in the rainy season. The variables among discrete fields with various periods under cultivation average temperature in the rainy season is 27.5 °C. managements (Kiyono et al., 2007; Moebius-Clune et al., 2011; Nyberg In Kenthao District of Sainyabuli Province, maize cultivation was et al., 2012). Nyberg et al. (2012) conducted a field investigation at introduced 30 years ago. The period of continuous maize cropping eight Kenyan sites with various maize cultivation periods to evaluate varied from 1 to 30 years among fields, depending on reclamation time, soil property trends under crop cultivation that had been operating for when the fields were converted from primeval or secondary forest. 120 years, and concluded C and N concentrations in soil dropped to During continuous cropping, only maize is cultivated in the rainy around 60% from the initial values. Similarly, Moebius-Clune et al. season; no crops were cultivated in dry season; and only one planting (2011) conducted research in several farmers’ fields to evaluate trends was harvested annually. Hybrid varieties of Charoen Pokphand Seeds in soil conditions and maize yield in Kenyan fields over 80 years, and Co. Ltd. were used in most farmer’s fields. Sowing was conducted in the − reported yield decrease of 2 t ha 1 over 12 years. period between May and June, after tillage. Grain and cobs were har- Crop yield is generally different based on topo-sequential positions. vested between September and November, with the stems and leaves Yield is better at lower positions than upper positions on a slope field left on the fields. No fertilizers or fallowing was conducted. These (Miller et al., 1988; Verity and Anderson, 1990). This yield difference is cultivation management methods were common to all farms in- due to the redistribution of soil from erosion and sedimentation during vestigated in this study. Soils in the study area are categorized into crop cultivation. Because maize production in northern Laos is pri- Acrisol, in the soil map of FAO taxonomy (1976), and Ultisol, in the marily conducted on sloping land, the effect of soil erosion and sedi- global soil regions map of USDA taxonomy (2005). mentation should be large. Given the topographical characteristics, In 2014 and 2015, 21 and 19 fields were respectively investigated in differences in yield trends due to topo-sequential positions need to be two villages (Fig. 1). Field size vary from 0.3 ha to 2 ha, and 0.9 ha in evaluated. average. Three sample sites were selected to equally distribute the slope The objective of this study is to evaluate maize productivity and soil with maximum angle for each field, and were categorized into four fertility under continuous maize cultivation in farmers’ fields in topo-sequential positions: upper, middle, lower, and flat positions, to Sainyabuli Province. To achieve this objective, we selected farmers’ evaluate the effect of geographical characteristics on yield trend under fields with varying periods of continuous maize cultivation and dif- continuous cultivation. The categorization first defi nes fields into two ferent topo-sequential positions. This first report showed the maize types: sloped (i.e., slope angles over 8°) and flat fields. The slope angle yield trend in relation to topo-sequential positions under continuous of the field was determined from the position information of three cultivation, and it discussed production sustainability in terms of yield sample sites measured with a global positioning system, and from cal- trend and economical balance assessment. culation using QGIS with data from Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model, ver. 2 (ASTER GDEM ver. 2; NASA, 2011). Next, sample sites of sloped 2. Methodology and measurement fields were categorized into upper, middle, or lower positions per the relative elevation of three sample sites at each field; the three sample Research was conducted in Sainyabuli Province, located in a sites of each flat field were categorized into flat positions. northern mountainous area (Fig. 1), where most farmers’ fields lay on Yield was quantified during the crop maturity season in September sloping land. The average annual precipitation in Saynyabuli province and October. Grain was collected from 3 × 3 m plots from where the is 1362 mm, of which 77% is recorded in the rainy season (i.e., May to

Fig. 1. Map of the study area, including the investigated fields and villages in Sainyabuli Province. The closed circle symbols represent the investigated maize fields. The triangle symbols represent villages.

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